The rectus abdominis muscle, () also known as the "abdominal muscle" or simply better known as the "abs", is a pair of segmented

skeletal muscle Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

on the

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

aspect of a person's

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

. The paired muscle is separated at the midline by a band of

dense connective tissue Dense connective tissue, also called dense fibrous tissue, is a type of connective tissue with fibers as its main extracellular matrix, matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows ...

called the linea alba, and the connective tissue defining each lateral margin of the rectus abdominus is the

linea semilunaris The linea semilunaris (also semilunar line or Spigelian line) is a curved line found on either side of the rectus abdominis muscle. History The linea semilunaris was first described by Adriaan van den Spiegel. Structure There are two common ...

. The muscle extends from the

pubic symphysis The pubic symphysis (: symphyses) is a secondary cartilaginous joint between the left and right superior rami of the pubis of the hip bones. It is in front of and below the urinary bladder. In males, the suspensory ligament of the penis attache ...

pubic crest Medial to the pubic tubercle is the pubic crest, which extends from this process to the medial end of the pubis (bone), pubic bone. It gives attachment to the conjoint tendon, the rectus abdominis, the abdominal external oblique muscle, and the ...

and

pubic tubercle The pubic tubercle is a prominent tubercle on the superior ramus of the pubis bone of the pelvis. Structure The pubic tubercle is a prominent forward-projecting tubercle on the upper border of the medial portion of the superior ramus of th ...

inferiorly, to the

xiphoid process The xiphoid process (), also referred to as the ensiform process, xiphisternum, or metasternum, constitutes a small cartilaginous process (extension) located in the inferior segment of the sternum, typically ossified in adult humans. Both the Gr ...

and

costal cartilages Costal cartilage, also known as rib cartilage, are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax. Costal cartilage is only found at the anterior ends of the ribs, prov ...

of the 5th–7th ribs superiorly. The rectus abdominis muscle is contained in the

rectus sheath The rectus sheath (also called the rectus fascia.) is a tough fibrous compartment formed by the aponeuroses of the transverse abdominal, transverse abdominal muscle, and the internal oblique, internal and external oblique muscles. It contains the ...

, which consists of the

aponeuroses An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

of the lateral abdominal muscles. Each rectus abdominus is traversed by bands of connective tissue called the

tendinous intersections The rectus abdominis muscle is crossed by three fibrous bands called the tendinous intersections or tendinous inscriptions. One is usually situated at the level of the umbilicus, one at the extremity of the xiphoid process, and the third about mi ...

, which interrupt it into distinct muscle bellies.

Structure

The rectus abdominis is a very long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba. Tendinous intersections (intersectiones tendineae) further subdivide each rectus abdominis muscle into a series of smaller muscle bellies. Tensing of the rectus abdominis causes the muscle to expand between each tendinous intersection.Abdomen, in Moore, K.L., Dalley, A.F., Agur, A.M.R. (eds). 2014. Clinically Oriented Anatomy: Seventh Edition. Lippincott Williams & Wilkins. Philadelphia. PA. pg:191. The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibers of insertion into the anterior extremity of the rib itself.

Size

It is typically around 10 mm thick, although, some athletes can have a rectus up to 20 mm thick. Typical volume is around 300 cm³ in non-active individuals and 500 cm³ in athletes.

Blood supply

The rectus abdominis has many sources of arterial blood supply. Classification of the vascular anatomy of muscles: First, the

inferior epigastric artery In human anatomy, the inferior epigastric artery is an artery that arises from the external iliac artery. It is accompanied by the inferior epigastric vein; inferiorly, these two inferior epigastric vessels together travel within the lateral um ...

and vein (or veins) run superiorly on the posterior surface of the rectus abdominis, enter the rectus fascia at the arcuate line, and serve the lower part of the muscle. Second, the

superior epigastric artery In human anatomy, the superior epigastric artery is a terminal branch of the internal thoracic artery that provides arterial supply to the abdominal wall, and upper rectus abdominis muscle. It enters the rectus sheath to descend upon the inner ...

, a terminal branch of the

internal thoracic artery The internal thoracic artery (ITA), also known as the internal mammary artery, is an artery that supplies the anterior chest wall and the breasts. It is a paired artery, with one running along each side of the sternum, to continue after its bifurc ...

, supplies blood to the upper portion. Finally, numerous small segmental contributions come from the lower six

intercostal arteries The intercostal arteries are a group of arteries passing within an intercostal space (the space between two adjacent ribs). There are 9 anterior and 11 posterior intercostal arteries on each side of the body. The anterior intercostal arteries a ...

as well.

Nerve supply

The muscles are innervated by thoraco-abdominal nerves, these are continuations of the T7-T11

intercostal nerves The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and dif ...

and pierce the anterior layer of the

. Sensory supply is from the 7-12

thoracic nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into t ...

Variation

The

sternalis muscle The rectus sternalis muscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis ...

may be a variant form of the pectoralis major or the rectus abdominis. Some fibers are occasionally connected with the

costoxiphoid ligaments The costoxiphoid ligaments (chondroxiphoid ligaments) are inconstant strand-like fibrous bands that connect the anterior and posterior surfaces of the seventh costal cartilage, and sometimes those of the sixth, to the front and back of the xiphoid ...

, and the side of the

Function

The rectus abdominis is an important postural muscle. It is responsible for flexing the

lumbar spine The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe t ...

, as when doing a crunch. The rib cage is brought up to where the

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

is when the pelvis is fixed, or the pelvis can be brought towards the rib cage (posterior pelvic tilt) when the rib cage is fixed, such as in a leg-hip raise. The two can also be brought together simultaneously when neither is fixed in space. The rectus abdominis assists with breathing and plays an important role in

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

when forcefully exhaling, as seen after exercise as well as in conditions where exhalation is difficult such as emphysema. It also helps in keeping the internal organs intact and in creating intra-abdominal pressure, such as when exercising or lifting heavy weights, during forceful defecation or parturition (childbirth).

Clinical significance

An abdominal muscle strain, also called a pulled abdominal muscle, is an injury to one of the muscles of the abdominal wall. A muscle strain occurs when the muscle is stretched too far. When this occurs the muscle fibers are torn. Most commonly, a strain causes microscopic tears within the muscle, but occasionally, in severe injuries, the muscle can rupture from its attachment. A

rectus sheath hematoma A rectus sheath hematoma is an accumulation of blood in the sheath of the rectus abdominis muscle. It causes abdominal pain with or without a mass. The hematoma may be caused by either rupture of the epigastric artery or by a muscular tear. Sev ...

is an accumulation of blood in the sheath of the rectus abdominis muscle. It causes

abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Since the abdomen contains most of the body's vital organs, it can be an indicator of a wide variety of diseases. Given th ...

with or without a mass. The

hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

may be caused by either rupture of the epigastric artery or by a muscular tear. Causes of this include

anticoagulation An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which h ...

coughing A cough is a sudden expulsion of air through the large breathing passages which can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ...

pregnancy Pregnancy is the time during which one or more offspring gestation, gestates inside a woman's uterus. A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Conception (biology), Conception usually occurs ...

abdominal surgery The term abdominal surgery broadly covers surgical procedures that involve opening the abdomen (laparotomy). Surgery of each abdominal organ is dealt with separately in connection with the description of that organ (see stomach, kidney, liver, e ...

and

trauma Trauma most often refers to: *Psychological trauma, in psychology and psychiatric medicine, refers to severe mental and emotional injury caused by distressing events *Traumatic injury, sudden physical injury caused by an external force, which doe ...

. With an ageing population and the widespread use of anticoagulant medications, there is evidence that this historically benign condition is becoming more common and more serious. On

abdominal examination An abdominal examination is a portion of the physical examination which a physician or nurse uses to clinically observe the abdomen of a patient for signs of disease. The abdominal examination is conventionally split into four different stages: ...

, people may have a

positive Positive is a property of positivity and may refer to: Mathematics and science * Positive formula, a logical formula not containing negation * Positive number, a number that is greater than 0 * Plus sign, the sign "+" used to indicate a positi ...

Carnett's sign In medicine, Carnett's sign is a finding on clinical examination in which ( acute) abdominal pain remains unchanged or increases when the muscles of the abdominal wall are tensed. For this part of the abdominal examination, the patient can be aske ...

. Most hematomas resolve without treatment, but they may take several months to resolve.

Other animals

The rectus abdominis is similar in most vertebrates. The most obvious difference between animal and human abdominal musculature is that in animals, there are a different number of tendinous intersections.

Additional images

File:Gray399.svg, Diagram of sheath of rectus abdominis File:Illu trunk muscles.jpg, Muscles of the trunk File:2018-10-07 MAG Training at 2018 Summer Youth Olympics (Martin Rulsch) 21.jpg, Male athlete with a visible rectus abdominis File:2014 DécaNation - 100 m 16.jpg, Female athlete with a visible rectus abdominis

References

External links

* – "Muscles of the anterior

chest wall The thoracic wall or chest wall is the boundary of the thoracic cavity. Structure The bony skeletal part of the thoracic wall is the rib cage, and the rest is made up of muscle, skin, and fasciae. The chest wall has 10 layers, namely (from ...

with the pectoralis major muscles removed." * – "Thoracic Wall: The Anterior Thoracic Wall" * – "Incision and reflection of the

external abdominal oblique The abdominal external oblique muscle (also external oblique muscle or exterior oblique) is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. Structure The external oblique is situated on the lateral ...

muscle." * – "Incision and reflection of the internal abdominal oblique muscle." * – "Anterior Abdominal Wall: The Rectus Abdominis Muscle" * * {{DEFAULTSORT:Rectus Abdominis Muscle Muscles of the torso Spine flexors Midriff